MI_3317-2e

MAINTENANCE INSTRUCTIONM.I. 3317-2

Revision E

Service DepartmentELECTRO-MOTIVE DIVISION

GENERAL MOTORS CORPORATIONOctober, 2001

AR10, AR12, AR15, AR16, AR17, TA12, TA17, TA20 andTA22

Traction Generator Rectifier Bank Assemblies andSuppression Circuits

SAFETY PRECAUTIONS

Please refer to the EMD Safety Precautions in Appendix to the LocomotiveService Manual whenever routine service or maintenance work is to be performed

on any AC traction-equipped locomotive.

The maintenance procedure as outlined in this instruction is specific to AR and TA-Type MainGenerators and is offered for planning purposes only. As written, this document reflects currentEMD product design and service experience for this design. The content of this MaintenanceInstruction reflects maintenance requirements based on time from delivery or miles in service.This recommendation is consistent with present fleet performance and remains within the EMDexperience envelope.

Traction / Rectifier Bank Assemblies 2 10/26/01

This Maintenance Instruction is intended to serve as a guide when establishingmaintenance schedules to meet the particular requirements of individual operations andplanned economic life of the AR and TA-type main generators. It provides averagerecommendations, which should ensure satisfactory locomotive operation, andeconomical maintenance costs where average load factors and climatic conditions areencountered.

The scheduled inspection and maintenance items defined herein are specific to the ARand TA-type main generators. Component renewal provisions are consistent withtraditional overhaul procedures.

For planning purposes, EMD has established the following overhaul intervalrecommendations for the main generators. These overhaul interval recommendations arebased on whichever event occurs first: time or miles.

AR and TA Series Main Generators:High Speed Service: 16 years / 2,500,000 miles /4,000,000 KilometersHeavy Haul Service: 16 years / 2,000,000 miles / 3,200,000 Kilometers

NOTEMileage values referenced above are defined by Microprocessor Archive Data when thelocomotive is equipped with a locomotive control computer system.

As usual, when specific operating conditions severely impact locomotive performanceand/or reliability, maintenance schedules must be adjusted accordingly.

Copyright 2001Electro-Motive Division, General Motors Corporation.

Prepared by International Technical Services London, Ontario, CanadaAll rights reserved. Neither this document, nor any part thereof, may be reprinted withoutthe expressed written consent of the Electro-Motive Division. Contact EMD ServicePublications Office.

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TABLE OF CONTENTS

1.0 AR10, AR12, AR15, AR16, AR17, TA12, TA17, TA20 and TA22 TractionGenerator Rectifier Bank Assemblies and Suppression Circuits.........4

1.1 INTRODUCTION .................................................................................................. 41.2 RECTIFIER INSPECTION.................................................................................... 8

1.2.1 CLEANING RECTIFIER BANK ASSEMBLY ............................................ 91.2.2 DIODE AND FUSE QUALIFICATION...................................................... 10

2.0 PROTECTIVE FUSES ..............................................................................192.1 FUSE RATING AND TEST VALUES................................................................ 20

2.1.1 FUSE TESTING ........................................................................................... 202.2 DIODE INSPECTION AND REPLACEMENT.................................................. 22

2.2.1 MIXING OF DIODES.................................................................................. 222.2.2 DIODE TESTING ........................................................................................ 222.2.3 FURTHER DIODE TESTS .......................................................................... 232.2.4 DIODE REPLACEMENT............................................................................ 24

2.3 DIODE CLASSIFICATION................................................................................. 262.3.1 DIODE POLARITY ..................................................................................... 262.3.2 DIODE TYPES............................................................................................. 272.3.3 DIODE VOLTAGE CLASSES .................................................................... 282.3.4 DIODE MATCHING.................................................................................... 29

3.0 COMMUTATION TRANSIENT VOLTAGE SUPPRESSION ....................323.1 INTRODUCTION ................................................................................................ 323.2 SUPPRESSION SYSTEM DESCRIPTION......................................................... 32

3.2.1 BRIDGE-CONNECTED SUPPRESSION CIRCUIT.................................. 323.2.2 DELTA-CONNECTED SUPPRESSION CIRCUIT.................................... 333.2.3 INSPECTION OF THE SUPPRESSION SYSTEM .................................... 34

3.3 TEST AND CORRECTIVE MEASURES........................................................... 343.3.1 LOOSE OR IMPROPER CONNECTIONS................................................. 343.3.2 DAMAGED RESISTORS............................................................................ 343.3.3 DEFECTIVE CAPACITORS....................................................................... 34

4.0 GENERATOR MODELS...........................................................................365.0 SERVICE DATA .......................................................................................50

5.1 DIODE APPLICATION (Universal Diodes) ....................................................... 505.2 CURRENT LIMITING FUSE APPLICATION................................................... 505.3 CURRENT LIMITING FUSE RESISTANCE VALUES (@75F/23C) ........... 505.4 REFERENCES ..................................................................................................... 515.5 SPECIFICATIONS............................................................................................... 515.6 EQUIPMENT LIST.............................................................................................. 51


1.0 AR10, AR12, AR15, AR16, AR17, TA12, TA17, TA20and TA22 Traction Generator Rectifier BankAssemblies and Suppression Circuits

CAUTIONDo not perform high potential tests on diodes, either individually or collectively.If a high potential test is to be performed on the locomotive or generator, allpositive and negative generator buses must be shorted together, and the brushesat the collector rings connected together to prevent high potential from beingapplied to the controlled rectifier assembly (SCR). Always refer to the applicableLocomotive Service Manual to perform a high potential test on a locomotive.Operation of the generator without load is not recommended, and should berestricted to an absolute minimum; but under no circumstances allow no-loadvoltage to exceed 800 VDC, and never operate the generator with the inspectiondoors open or panels removed.

1.1 INTRODUCTION

NOTEThe AR8, AR11, AR11A, and AR20 Traction Generator Rectifier BankAssemblies and Suppression Circuits are covered in Maintenance Instruction MI3317-3. MI 3318 is dedicated to AR5, and AR6 Main Generator is coveredunder MI 3323. Main Generator assemblies equipped with a Head EndGenerator are covered under MI 3319.

The traction generator is a three-phase alternator, the rotor of which makes up a10 pole DC excited field. Two sets of Y-connected windings make up thealternator stator. The arrangement results in two separate sources of three-phaseAC output, each independently rectified by an assembly of heat-sink mountedsilicon diodes. Two types of rectifier assembly frames are now being used. Thefabricated-type frame is shown in Figure 1. The molded-type frame is shown inFigure 2.

Fuses are provided to isolate diodes that may become shorted. On the AR-typeMain Generator discussed in this Maintenance Instruction, the operating coil of aprotective relay (GR), is connected across the neutral points of the statorwindings to detect a single phase or imbalance condition. On all the TA-typeMain Generators, a ground relay transductor (GRT) and a transformer (T2) areused in conjunction with the ground relay to detect an open phase or imbalancecondition. The ground relay coil is also connected through resistance to groundto detect High Voltage Grounds (Generator / Traction Motors [AC and DC] /Inverters or locomotive grounds).

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At the collector ring end of the machine, one rectifier bank assembly is to the leftand the other to the right of the slip rings. Each assembly consists of:

1. A positive and a negative heat sink and bus bar assembly.2. A mounting frame.3. An equal number of positive base diodes and negative base diodes.4. Interrupting fuses.

Capacitors and resistors for suppression of voltage spikes of a transient natureare located within the generator airbox, either on the airbox wall or on thegenerator end housing. Refer to Figure 3 and Figure 4.

NOTETA 20 and TA 22 Main Generators do not have a suppression circuit.

Most models of Main Generators are equipped with current transformersmounted on the generator end plate. On TA12, TA17 and all AR-type MainGenerators (when equipped) there are three transformers, one per phase (A,B, and C), installed on one of the stator winding set at the AC side of arectifier bank. AC current as sensed by the transformers is proportional to DCcurrent at the main generator buses. As such, it provides a signal that isproportional to DC current output from the main generator.

Models TA20 and TA22 Main Generators are dual output generators, meaningthat each of the two stator winding outputs is connected directly to a differentinverter. The two stator winding sets are not paralleled, and therefore 6 currenttransformers are being used on these Main Generators (Three per winding set).

When the locomotive control system is equipped with a performance controlpanel (PCP), or a performance control module (Dash-2 control system), thegenerator- mounted current transformers, along with cabinet-mounted potentialtransformer(s), provide signals for control of generator excitation and poweroutput.

On those AR10 generators that are not equipped with current transformers(CTs), a cabinet-mounted main generator field current transductor provides thenecessary signals for control of generator output. The use of field current toprovide a signal related to output is possible because the characteristics of thegenerator are such that for much of the generator operating range generatoroutput increases directly as field current increases.


When a locomotive is equipped with a locomotive control computer (LCC), thesignals from the CTs are used, along with other feedback devices, to controlMain Generator field excitation, as well as to monitor Main Generator outputcurrent.

CAUTIONSome generators may be equipped with current transformers that are not used.The secondary winding of these unused current transformers must be shortedtogether to prevent high voltage damage to the generator.

Model AR16 generators have one larger current transformer mounted on thegenerator end plate. The single transformer monitors all of the AC current fromphase A of one rectifier bank. Refer to Figure 5 to Figure 12 for a simplifiedpictorial wiring diagram of the AR and TA- type main generators discussed inthis maintenance instruction.

Figure 1 Fabricated-Type Rectifier Bank Assembly

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Figure 2 Molded-Type Rectifier Bank Assembly

Figure 3 Fabricated-Type Rectifier Assembly in Place


Figure 4 Molded-Type Rectifier Assembly in Place

1.2 RECTIFIER INSPECTION

The rectifier assembly should be inspected at intervals indicated in theScheduled Maintenance Program. Refer to Figure 13 to inspect the rectifierassembly.

IMPORTANT NOTICEIt is recommended that the fuses and diodes in any given model generator bereplaced after 10 years of service due to thermal/mechanical degradation

SAFETY PRECAUTIONSPlease refer to the EMD Safety Precautions in Appendix to the LocomotiveService Manual whenever routine service or maintenance work is to beperformed on any AC traction-equipped locomotive.

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1.2.1 CLEANING RECTIFIER BANK ASSEMBLY

The following procedure is recommended for cleaning the rectifier assemblies.The cleaning should be performed at the intervals stated in the ScheduledMaintenance Program.

1. Remove the heat sink assemblies from the generator. Ensure all cables andwires are labeled before disconnecting.

2. Remove all fuses from rectifier banks to prevent damage to fuses duringcleaning operation. If there is no visible damage to diodes, diodes shouldremain in heat sinks. If there is reason to remove diodes before cleaning,inserts such as discarded diodes should be placed in diode holes to protectdiode contact surface on the heat sinks. Use special diode wrench to removediodes. Refer to Service Data for diode-wrench part number.

WARNINGWater or cleaning solution allowed to contaminate the arc quenching sand insidethe fuse body can cause the fuse to explode when it is required to isolate ashorted diode.

3. Mix a steam cleaner such as Dober Chemical Corporation Cleaner 6006, orTurco Chemical Company Steamfas in a suitable container. Use an 85-g per3.79-liter (3 oz. per gal.) mixture of cleaner and water and maintain a tanktemperature of approximately 60C to 71C (140F to 160F).

WARNINGProtect skin and clothing while steam cleaning. Operator should always wearrubber apron, boots, gloves, and a plastic face shield.

4. Place steam gun suction-pipe into the cleaning solution and regulate the gunto obtain a good soapy solution.

CAUTIONDo not use live steam alone to clean the assemblies, and do not soak theassemblies in a caustic solution. If diodes are removed from the heat sink, thecontact surfaces of the diodes and heat sink assemblies must not be cleaned withan abrasive material or wire brush. Such cleaning will destroy the finish andreduce heat rejection capability.

5. Clean all parts of the heat sink assembly, keeping the gun nozzle 100 to 150mm (4 to 6) from the work.

6. Thoroughly rinse the assembly with a low-pressure stream of clean water toremove all residues.


7. Blow off remaining clean water with dry air.

8. After cleaning, the assembly should be checked for flash damage, or damagecaused by shorting to ground. If damage has occurred, dismantle theassembly and replace any defective parts with new parts. (Always refer toparts catalogue to disassemble or reassemble a rectifier bank assembly.) If nodamage is found, the assembly will not need to be dismantled.

1.2.2 DIODE AND FUSE QUALIFICATION

Check all diodes using the following procedure:

1. Connect one of the ohmmeter leads on the negative bus, and with the otherlead check every diode connected to the bus. Then switch the tester leads andcheck every diode again. This checks all the negative base diodes.If diode is good, the meter registers 10 to 20 ohms in one direction, andabove 30,000 ohms when leads are reversed.

2. Connect one of the ohmmeter leads on the positive bus and with the otherlead check every diode connected to the bus. Then switch the tester leads andcheck every diode again. This checks all the positive base diodes.If diode is good, the meter registers 10 to 20 ohms in one direction andabove 30,000 ohms when leads are reversed.

3. Remove any defective diodes, using special diode socket (See Service Datafor socket number)

4. Wipe the diode-mounting surface of the heat sink bus. Do not use abrasivematerial.

5. Replace defective diodes with good diodes of identical polarity, and voltageclass (or higher voltage class). Apply a thin coating of compound 8346481 tothe base of the diode hex to cover the surface. Do not apply on threads.

6. With special diode socket and 0 50 ft.-lbs. Torque wrench, torque diodes to45 to 47 Nm (33 to 35 ft.-lbs.). Make certain that the wrench is properlyseated when torquing.

7. Check all fuses with continuity tester. Clean the electrical contact surfaces ofthe fuses as required, and reapply.

8. Torque diode terminal lug bolts to between 15 to 18 Nm (11 to 13 ft.-lbs).

Figure 5 through Figure 12 illustrate simplified drawings of the wiring schematictypical for AR and TA style generators.

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Figure 5 Simplified AR10, AR12, and AR15 Pictorial Diagram

Figure 6 Simplified AR10E2 Pictorial Diagram


Figure 7 Simplified AR16 Pictorial Diagram

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Figure 8 Simplified AR17 Pictorial Diagram


Figure 9 Simplified TA12 Pictorial Diagram

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Figure 13 Rectifier Inspection

NOTEModels AR10E2 and TA20 have 24 fuses (4 at each port). Model AR16 has 48fuses (8 fuses at each port). All the other models covered by this maintenanceinstruction have 30 fuses (5 at each inspection port).

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Figure 14 Current Limiting Fuse- Round Type

Figure 15 Current Limiting Fuse- Square Type (applied to TA20 and TA22)

2.0 PROTECTIVE FUSESCurrent limiting fuses, Figure 14 and Figure 15, are provided to isolate shorteddiodes. The fuses are a bolted-lug type, with the lugs affixed to end blocks. Fastacting silver alloy fusible links, attached to the end block, are surrounded withsilicon sand that acts to absorb arc energy during fault clearing. The body of thefuse is made of reinforced melamine.

On the round-type fuse, a small indicating fuse is affixed to the main fuse body,and is connected in parallel with the main fuse elements. When the mainelements burn open, the element of the indicator also burns open. A spring in theindicator drives an indicating pin to protrude about 5 mm (3/16) from the end ofthe indicator. The operating principle remains the same for the square type,except that the indicator pin is part of the fuse main body.


NOTEThe internal-hex screw on one end of the fuse is provided only for insertion ofsand by the manufacturer. The screw is staked to prevent its removal. Thefusible elements cannot be renewed, and a blown fuse cannot be repaired.

2.1 FUSE RATING AND TEST VALUES

PART # CURRENTRATING

GENERATORMODEL

NOTES

8346478 350 Amps AR6, AR7, AR10, AR 12 Original Equipment8407729 400 Amps AR15, AR17, TA12, TA17 Original Equipment40054000 315 Amps TA20, TA22 Original Equipment40080476 600 Amps AR6, AR7, AR10, AR12

AR15, AR17, TA12, TA17Replaces Fuses8346478 and 8407729

Table 1 Table Current Limiting Fuses and Rating


GENERATORMODEL

RESISTANCEVALUES

8346478 350 Amps AR6, AR7, AR10, AR 12 .000195 + - .0000108407729 400 Amps AR15, AR17, TA12, TA17 .000195 + - .00001040054000 315 Amps TA20, TA22 .000368 + - .00001040080476 600 Amps AR6, AR7, AR10, AR12

AR15, AR17, TA12, TA17.000195 + - .000010

Table 2 Fuse Resistance Values

2.1.1 FUSE TESTING

Thermal and mechanical loads could subsequently break the fusible links insidethe fuse body. There are normally 6 links per fuse that will equate to theresistance value provided in table 2. If any of the fuse links should break and orburn open, it will change the resistance value, which will warrant replacementof the fuse. If not detected, a whole phase group of fuses could fail and result inan imbalance condition. This will result in pick-up of the ground relay and areduction of load to the locomotive.

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The resistance check must be performed with the use of a low resistanceohmeter, capable of taking readings as low as 1.999 milliohms. (ReferenceService Data for part number of tester). Due to the use of silver links in thesefuses verses copper, it is very important that the correct temperature of the fusebe determined, or the fuse could fall outside the limits and a good fuse may showit is defective. As a rule of thumb, if at least one link is open, the resistance valuewill increase by at least 25 %.

NOTEThe values listed in table 2 are taken at 75 degrees F, 23 degrees C. Important totest the fuses at this temperature range to achieve an accurate value.

Figure 16 Diode Inspection and Replacement (Diodes must be matched if universal typediodes are not used)


2.2 DIODE INSPECTION AND REPLACEMENTRefer to 1.2 for information regarding diode testing and replacement. Use thefollowing procedures for testing and replacement of diodes.

2.2.1 MIXING OF DIODESThis is with respect to the release of the universal diodes P/N 40029132 (Pos)and 40029131 (Neg). These diodes will not permit desired sharing of loadcurrent when paralleled with any other previous used (Typed Diodes). In orderto insure proper current sharing, a 5-for-5, 4-for-4, or 8-for-8 replacementper phase group, (dependant on Alternator model) should be done for thepolarity diodes involved. It is not necessary to replace both polarities, or bothsides of a phase group, as long as no failures need changeout. Those devicesremoved, and found to be still functional, may be retained and used as spareparts.

When an alternator is equipped with the black band universal diode and a failureof one or more occurs, it is NOT necessary to change the entire group of diodes.Only change the failed diode(s) and associated fuses in that particular phasegroup. Other associated diodes in that phase group that did not fail will not beaffected by the diodes that did fail.

2.2.2 DIODE TESTING

1. Remove the bolt and unfasten diode lead. Check fuse continuity.

NOTEIf multiple failures have occurred in a single group of diodes, or if repeatedfailures have been observed in a single group of diodes, isolate and check alldiodes in the group.

2. Place continuity tester across negative bus and connecting rod, thenswitch the tester leads. This checks one of the diodes.

3. If the diode is good, the meter registers 10 to 20 ohms in one directionand above 30,000 ohms when leads are reversed.

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NOTEThe 30,000-ohm value is for an individual diode isolated from the circuit. Adiode not isolated from the circuit should register greater than the followingvalues:

AR16 1250 ohmsAR10E2 2500 ohmsAll others 2000 ohms

4. Place continuity tester across positive bus and diode lead, then switch thetester leads. This checks the other diode.

Diode resistance depends, in a non-linear way, on applied voltage. Thecontinuity tester applies very little voltage across the diodes. Therefore, if theabove test is not conclusive, refer to Section 2.2.3 - Further Diode Tests.

2.2.3 FURTHER DIODE TESTSDiode testing with a continuity tester may not prove conclusively whether adiode is good, shorted or open. To make a better determination, the followingthree tests can be used:

2.2.3.1 DC Megger TestUse a hand-cranked or battery operated megohmmeter to test the diode. Connectone lead to diode pigtail and other lead to base of diode. If using a hand crankmeter, it is important to crank slowly at first, then gradually increase thecranking speed to medium. Depending on polarity, the reading should be zero(blocking) when connected one way, then by reversing test leads, there should bea definite megger reading of at least one megohm or better.

NOTERemember, you are checking to see if the diode is blocking and/or carryingcurrent. You are not taking insulation resistance readings, so a higher than onemegohm is not important.


2.2.3.2 DC Voltage TestConnect a 110-volt incandescent lamp in series with the suspected diode, andapply 64 vdc (from the locomotive batteries) to this series connected circuit,then, reverse diode leads and observe the lamp response.

If the diode is good, a light turns ON when the diode is connected oneway, and turns OFF when connected the other way.

If the lamp turns ON both ways, the diode is shorted out. If the lamp remains OFF when the diode is connected both ways, the

diode is open circuit.

2.2.3.3 AC Voltage TestConnect a 60 to 100-watt, 110-volt incandescent lamp in series with the suspectdiode. Apply 110-115 volts, 60-hertz shop power to the circuit, then reversediode leads and observe the lamp response.

If the diode is good, the lamp turns ON at about half of its normal lightlevel (half wave rectification), when the diode is connected in onedirection, and is OFF when connected the other way

If the lamp is close to full light level, the diode is shorted. If the lamp does not light, the diode is open.

2.2.4 DIODE REPLACEMENT1. Replace blown fuse with a good fuse.2. Remove any defective diodes, using special diode socket 8361524 or

40045217 (AR20/TA20/TA22), Figure 17 and Figure 18.3. Wipe the diode-mounting surface of the heat sink bus. Do not use

abrasive material.4. Replace defective diodes with good diodes of identical polarity and

voltage class (or higher voltage class). Apply a thin coating of compound8346481 to the base of the diode hex to cover the surface. Do not applyon threads.

5. With special diode socket and 0 50 ft.-lbs. Torque wrench, torquediodes to 45 to 47 Nm (33 to 35 ft.-lbs.). Make certain that the wrench isproperly seated when torquing.

6. Reapply the insulating boot and sleeve. Replace if burnt, cracked ordamaged.

7. Torque diode terminal lug bolts to between 15 to 18 Nm (11 to 13 ft.-lbs).

8. Replace and securely fasten all air box panels and inspection covers.

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Figure 17 Diode Socket for Standard Alternators

Figure 18 Diode Socket for AR20, TA20, and TA22 Alternators


2.3 DIODE CLASSIFICATIONFor service purposes, the following classifications of generator diodes aresignificant.

Polarity with respect to the diode base (threaded stud). A color code isused to assist in identification (See Diode Polarity 2.3.1).

Forward voltage drop (See Diode Types 2.3.2) Voltage class in respect to repetitive and non-repetitive peak inverse

voltage rating. Identification is assisted by color code (See DiodeVoltage Classes 2.3.3).

2.3.1 DIODE POLARITYThe direction in which conventional electrical current flows through a diodedetermines its polarity. The graphic arrow symbol, Figure 19, is oriented toindicate diode polarity.

Figure 19 Diode Polarity Symbol Negative Base Diode Shown

To provide a permanent method of identification, the ceramic cases of the diodesare permanently colored as follows:

DIODE POLARITY IDENTIFICATIONPositive BaseDiode

White Ceramic orPlain Metallic Case

Negative BaseDiode

Pink Ceramic orColor Band

Table 3 Diode Polarity Identification

For the diode to conduct, a positive voltage must be applied coincident with thetail of the arrow, and a negative voltage applied coincident with the point of thearrow. If the voltages are reversed, the diode will block, and only a small leakagecurrent will pass through the diode.

Negative base diodes require a positive voltage on the stud and anegative voltage on the flexible lead in order to conduct.

Positive base diodes require a positive voltage on the flexible lead, and anegative voltage on the stud.

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2.3.2 DIODE TYPES

Diodes are connected in parallel conducting paths. When parallel operation ofsilicon diodes is undertaken, means must be provided to ensure a reasonabledegree of current sharing. Each diode in a parallel group must share the load toprevent overloading of diodes in parallel with it.

Current sharing of generator diodes is accomplished by paralleling only diodeswhose forward characteristics (forward voltage drops), are a near match.

NOTEThe universal-type diodes being used now, have the same forwardcharacteristics, and no longer need to be matched.

In the past, diodes were segregated under specific test conditions, according totheir forward characteristics, and were assigned a type number that waspermanently impressed in the metal at the flat end of the threaded stud. Inaddition, a color-coded band was applied where the flexible lead is crimped tothe diode body.

DIODE TYPENUMBER

BODY CRIMP COLORBAND

1 None2 Red3 Black

Table 4 Former Diode Types

NOTEOnly 3 Universal Diodes without type identification (with different voltageclasses), available as replacement parts, are being used on current production ofAR and TA-type main generators.However, on main generators NOT equipped with universal type diodes, ifdiode(s) with a type # need to be changed within a matched group, thereplacement diode(s) need to be of the same type as the others within the group.If this is not possible, ALL of the matched diodes will have to be replaced byuniversal type diodes.

NOTEIt is recommended that any former types diodes in any given model generator bereplaced as the universal diode was introduced in 1991. All diodes should bereplaced after 10 years of service due to thermal/mechanical degradation


2.3.3 DIODE VOLTAGE CLASSESSix voltage classes of diodes have been manufactured in the past and are nowbeing replaced by three universal type diodes. The class identification isindicative of repetitive and non-repetitive transient peak, inverse voltagecapabilities, under specific test conditions. Diodes used in the past had a colorband around the barrel at the lug end of the flexible lead to indicate the diodevoltage class. The universal diodes used today do not have a color band, and canonly be identified by the part number impressed on the diode casing. Tables 4and 5 will assist in diode identification.

COLOR BAND(AT LUG BARREL)

VOLTAGECLASS

None 1600/2000Orange 1800/2100Green 2000/2400Brown 2200/2600Blue 2200/2800

White 2200/3000Table 5 Diode Voltage Classes (on older equipment)

VOLTAGECLASS

PART NUMBER APPLICATION

2600 Volts 40032602 Pos.40032603 Neg.

AR20

2800 Volts 40029132 Pos.40029131 Neg.

All AR, TA12, TA17

4400 Volts 40053999 Pos.40053998 Neg.

TA20, TA22

Table 6 Diode Voltage Classes (new type universal diodes)

The voltage class used in a specific generator is dependent upon the type ofservice in which the generator is employed, and upon specific characteristics ofthe control system that is used.

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2.3.3.1 Manufacturers Qualification MarksThe manufacturer has placed a variety of qualification marks upon diodes. Someof these qualification marks include: small color dots on the diode body, largecolor spots (not bands) on the diode body or lug, color marks at the edge of thelug, and numbers stamped onto the diode body. These marks are for themanufacturers identification only. The only significant marks for servicepurposes are:

The service part number printed on the cap of the diode body. The color of the ceramic insulator.

ALL OTHER COLOR SPOTS AND STAMPINGS ARE IRRELEVANTFOR SERVICE PURPOSES, AND ARE TO BE COMPLETELYDISREGARDED.

2.3.4 DIODE MATCHINGFigure 22 shows a typical AR10 rectifier assembly with the air box removed.The illustration shows how diodes and fuses are paralleled, in groups of five, byuse of paralleling bars. Diodes used in the generator must be matched as follows:

PolarityAll diodes in any paralleled group must be of the same polarity (ceramic casesmust be of the same color), and the diodes must be applied to the proper heat-sink bus. Negative base (pink) diodes to negative bus, and positive base (white)diodes to positive bus. Bus polarity is stamped into the end of the bus.

Type (applicable to non-universal diodes only)All diodes in any paralleled group should be of the same type (same impressedtype number and same type color band at the lower crimp). MIXING OFTYPES WILL CAUSE UNEQUAL LOAD SHARING. Observe thathexagonal connecting rods do not connect diodes in parallel; therefore, diodesconnected by rods do not necessarily match by type.


NOTEOnly 3 Universal Diodes without type identification (with different voltageclasses), available as replacement parts, are being used on current production ofAR and TA-type main generators.However, on main generators NOT equipped with universal type diodes, ifdiode(s) with a type # need to be changed within a matched group, thereplacement diode(s) need to be of the same type as the others within the group.If this is not possible, ALL of the matched diodes will have to be replaced byuniversal type diodes.

Voltage Class Diodes of different voltage classes may be mixed in a generator, but all diodesin any generator must equal to, or better than the inverse voltage ratings (voltageclass) required for the particular application. For example, diodes of the 4400volts voltage class may be mixed with diodes of the 2800 volts voltage class butnot the reverse.

Figure 20 Non-Universal Diode Identification Markings

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Figure 21 Universal Diodes Identification Markings

Figure 22 Diode Matching Within Groups (applicable to non-universal diodes only)


3.0 COMMUTATION TRANSIENT VOLTAGESUPPRESSION

3.1 INTRODUCTIONThe action of diodes switching from a conducting to a blocking state in thegenerator is called commutation. During commutation, high reverse currentflows in the diodes for a few microseconds, after which time the value of reversecurrent flow in the diode suddenly drops to almost zero. After commutation,voltage transients are produced.

The rate at which current flow changes from a high value to almost zero,multiplied by circuit inductance determines the magnitude of the transientvoltage spike. If this transient voltage exceeds the reverse rating of the diode, thediode will immediately fail.

With the exception of the TA20 and TA22 main generators, all of the othermain generators discussed in this maintenance instruction, are actually equippedwith a system for capacitive storage of energy from circuit inductance duringcommutation. The system is called the Commutation Transient VoltageSuppression System.

3.2 SUPPRESSION SYSTEM DESCRIPTIONTwo different suppression systems have been applied to protect the rectifiersfrom commutation transients. They are the Bridge-Connected SuppressionCircuit, and the Delta-Connected Suppression Circuit. Both provide equalreliability and protection when properly connected.

3.2.1 BRIDGE-CONNECTED SUPPRESSION CIRCUITThe first of these systems, the Bridge-Connected Suppression Circuit, Figure 23,uses a 4 microfarad capacitor, and a 10 ohms resistor connected in series andparallel with each group of five diodes for suppression of commutationtransients. Since the DC buses are paralleled, there are 12 series resistor-capacitor circuits connected in parallel with diodes.

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Figure 23 Bridge-Connected Suppression Circuit, Simplified Diagram

3.2.2 DELTA-CONNECTED SUPPRESSION CIRCUITThe second system, the Delta-Connected Suppression Circuit, Figure 24, uses a2 microfarad capacitor and a 5 ohms resistor connected in series for suppressionof commutation transients. These in turn are connected between the A, B,and C phase paralleling bars on both the left and right banks of the generator.

Figure 24 Delta-Connected Suppression Circuit, Simplified Diagram


3.2.3 INSPECTION OF THE SUPPRESSION SYSTEMAn inspection of the Commutation Transient Voltage Suppression Systemshould be made every time a faulty or failed diode is detected and replaced. Therequired inspection is basically visual. The following checks should be made.

1. Check that all connections are tight and are electrically correct.2. Examine all resistors for evidence of overheating and open turns.3. Examine all capacitors for oil leaks or deformation of the container. (The

container top may be badly pushed out).

3.3 TEST AND CORRECTIVE MEASURES3.3.1 LOOSE OR IMPROPER CONNECTIONS

Tighten any loose connections in accordance with the applicable wiring diagram.

3.3.2 DAMAGED RESISTORSAny resistors that appear to be burned or damaged should be disconnected andcontinuity checked. Faulty resistors must be immediately replaced with qualifiedresistors.

3.3.3 DEFECTIVE CAPACITORSIf a capacitor is suspected faulty, it should be disconnected and checked in thefollowing manner with a 500 or 1000 volt megger.

Short circuit the capacitor terminals and connect the positive lead from themegger to the terminals. Connect the megger negative lead to the capacitor case,and rotate the megger handle. The reading should be 25 megohms or more.Disconnect the megger and shorting jumper.Connect one megger lead to one capacitor terminal, and connect the othermegger lead to the other capacitor terminal, and rotate the megger handle. If thecapacitor is good, there will be a definite meter needle deflection toward zero(indicating capacitor charging current), followed by a drift toward infinity as thecapacitor charges. Failure of the meter needle to deflect toward zero is anindication that the capacitor is open internally.

If the capacitor is shorted, the megger will indicate zero when the megger handleis rotated. If the capacitor is open, it will indicate infinity immediately uponrotating the handle, and the reading will drop to zero when the rotation of thehandle is stopped.

M.I. 3317-2E 35 10/26/01

CAUTIONCarefully discharge the capacitor after the test, by using a screwdriver with aninsulated handle to short across the capacitor terminals.

If a 500 volt megger check indicates a good capacitor, but the condition of thecapacitor is still suspect (burn spots appear on resistors associated with thecapacitor), repeat the test with a 1000 volt megger. If the 1000 volt megger is notavailable, use a 64 VDC input, 1200 VDC output MG set, as a high potentialtester to induce possible flashover within the capacitor. Use the followingprocedure to perform the test:

1. Connect the positive output lead from the MG set to one terminal of thecapacitor. Connect the negative output lead from the MG set to the othercapacitor terminal. Connect a 0 1500 VDC meter to read MG setoutput voltage. Connect MG set input to a 64 or 74 VDC source.

2. Advance MG set output voltage The meter needle will advance as theMG set handle is rotated. If a flashover is induced in the capacitor, themeter needle will dip toward zero, indicating a bad capacitor.Immediately reduce voltage to zero, then turn off the MG set.

If the capacitor is good, voltage will remain at the high output value from theMG set. Reduce MG set voltage to zero, then turn off the set.

CAUTIONCarefully discharge the capacitor after the check, by using a screwdriver with aninsulated handle to short across the capacitor terminals.

WARNINGPolychlorinated Biphenyl (PCB) capacitors contain a toxic environmentalcontaminant requiring special handling and disposal in accordance with U.S.Environmental Protection Agency Regulations 40 CFR 761. For disposalinformation, contact the nearest U.S. EPA Office.

PCB capacitors are no longer available as replacement parts.

'


ORIGINAL PCBCAPACITOR

NON-PCB REPLACEMENTCAPACITOR

8380921 93320148442069 *9332014

(*requires bracket 8391246)8411555 93320168352261 9503808

Table 7 PCB Capacitor Replacement

4.0 GENERATOR MODELSThe particular model number assigned to a generator is determined byconsidering a variety of characteristics.

The type of suppression circuit employed, and the rating of suppressioncircuit components.

The use of, or lack of current transformers. The voltage class of the diodes employed. Configuration of air box. Type of coupling disc employed. Application of wedges at the rotor coils.

Refer to Figure 25 through Figure 37 for Physical Schematic Diagrams of ModelAR6, AR10, AR12, AR16, AR17, TA12-8, TA17-6 , TA20 and TA 22 rectifierbanks and suppression circuits.

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M.I. 3317-2E 37 10/26/01

Figure 25 AR10A Physical Schematic


Figure 26 AR10 Physical Schematic (Various Models)

M.I. 3317-2E 39 10/26/01

Figure 27 AR10 Physical Schematic (Various Models)


Figure 28 AR10B Physical Schematic

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Figure 29 AR10E2 Physical Schematic


Figure 30 AR10A7B, AR10A9 Physical Schematic

M.I. 3317-2E 43 10/26/01

Figure 31 AR10X2, AR12, AR12A, AR15, AR15A, Physical Schematic


Figure 32 AR16 Physical Schematic

M.I. 3317-2E 45 10/26/01

Figure 33 AR17 Physical Schematic


Figure 34 TA12-8 Physical Schematic

M.I. 3317-2E 47 10/26/01

Figure 35 TA17-6 Physical Schematic


Figure 36 TA20 Physical Schematic

M.I. 3317-2E 49 10/26/01

Figure 37 TA22 Physical Schematic


5.0 SERVICE DATA5.1 DIODE APPLICATION (Universal Diodes)

VOLTAGECLASS

PART NUMBER APPLICATION

2600 Volts 40032602 Pos.40032603 Neg.

AR20

2800 Volts 40029132 Pos.40029131 Neg.

All AR, TA12, TA17

4400 Volts 40053999 Pos.40053998 Neg.

TA20, TA22

5.2 CURRENT LIMITING FUSE APPLICATION


GENERATORMODEL

NOTES

8346478 350 Amps AR6, AR7, AR10, AR 12 Original Equipment8407729 400 Amps AR15, AR17, TA12, TA17 Original Equipment40054000 315 Amps TA20, TA22 Original Equipment40080476 600 Amps AR6, AR7, AR10, AR12

AR15, AR17, TA12, TA17Replaces Fuses

8346478 and 8407729

5.3 CURRENT LIMITING FUSE RESISTANCE VALUES(@75F/23C)


GENERATORMODEL

RESISTANCEVALUES

8346478 350 Amps AR6, AR7, AR10, AR 12 .000195 + - .0000108407729 400 Amps AR15, AR17, TA12, TA17 .000195 + - .00001040054000 315 Amps TA20, TA22 .000368 + - .00001040080476 600 Amps AR6, AR7, AR10, AR12

AR15, AR17, TA12, TA17.000195 + - .000010

M.I. 3317-2E 51 10/26/01

5.4 REFERENCES

AR8, AR11 and AR20 Traction Generator Rectifier Bank Assembliesand Suppression Circuit......................................................................... MI 3317-3Traction Alternators with Head End Power...............................................MI 3319AR5 Traction Generator.............................................................................MI 3318AR6 Traction Generator.............................................................................MI 3323

5.5 SPECIFICATIONS

Weight of Rectifier Bank Assembly (Approximate)AR10, AR12, AR15, AR6.............................................................. 45 kg. (100 lbs)AR16............................................................................................... 82 kg. (180 lbs)AR17............................................................................................... 45 kg (100 lbs)TA12-8............................................................................................ 45 kg (100 lbs)TA17-6............................................................................................ 45 kg (100 lbs)TA20............................................................................................... 64 kg (140 lbs)TA22................................................................................................ 64 kg (140 lbs)

5.6 EQUIPMENT LISTPart No.

Special Diode Socket 1 Hex (all standard AR).................................8361524Special Diode Socket 1 Hex (AR20/TA20/TA22) ........................ 40045217Torque Wrench 0 50 ft/lbs. 1/2 Drive ................................................8375396Compound Joint.......................................................................................8346481Multimeter ..................................................................................................8276478Megger Tester, 0 200 megohms at 500 VDC .........................................8174880Leads, 3.7 m (12 ft.) ...................................................................................8174878Carrying Case .............................................................................................8174879Dynamotor (MG Set) 1200 VDC Output 64 VDC Input .......................8233558Digital Low Ohm Resistance Tester Kit(Range 0 to 1.999 miliohms)..................................................................... 9322573(Includes AC DC Power Supply and 6 foot test leads)

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Document Number MM001001 (DE-LP)

Electro-Motive Division of General Motors CorporationLa Grange, Illinois 60525 USATelephone: 708-387-6000Website: www.gmemd.com

2001Electro-Motive Division, General Motors Corporation. All rights reserved.Neither this document, nor any part thereof, may be reprinted without theexpressed written consent of the General Motors Locomotive Group. ContactEMD Customer Publications Office.

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